Pennsylvania is among the nation's leaders in bridges that both lack backup protection against collapse in case a single, vital component fails and are designated by highway officials as being in need of repair, an Associated Press review of national bridge records found.

An Internet meme about the Fort Pitt Bridge has gone viral. It shows a picture of the outbound lanes and says, "Left lanes need to exit right, right lanes need to exit left. Here’s 300 feet to make it happen."

Some are among the busiest in the state, including the 85-year-old Liberty Bridge, spanning the Monongahela River from downtown Pittsburgh to its south side, and an Interstate 95 span in Philadelphia's lower northeast section along the Delaware River.

Others are on the Pennsylvania Turnpike.

Fewer than a third are state-owned, with many owned by county and municipal governments or railroads.

Pennsylvania has 577 such bridges, according to a state Department of Transportation list, although one, the Walt Whitman Bridge connecting South Philadelphia to New Jersey, was fixed over the past year and is no longer considered in need of repair by its owner, the Delaware River Port Authority.

The list has shrunk from the 646 that Pennsylvania reported to the federal government in 2011, a decrease PennDOT officials say has to do with extra money set aside in recent years to fix its most troublesome bridges.

But that extra money -- some of it borrowed against future bridge construction funds, some of it a one-time injection of federal economic stimulus money -- is gone and, if nothing changes, the total of bridges that are considered both "fracture critical" and "structurally deficient" is unlikely to drop substantially, PennDOT officials said.

If anything, the state is staring at a projected annual increase of 100 structurally deficient bridges as the deterioration of the state's aging bridges accelerates past the amount of money available to fix or replace them.

"We were getting to over 1,000 bridges a year for three years straight," said Scott Christie, PennDOT's deputy secretary for highway administration. But now, "we can barely afford to do 200 bridges a year going forward, so that number (of structurally deficient bridges) is going to start increasing like it was 10 years ago. We're going to completely lose everything we worked for over the last five years."

Christie said that any bridge in Pennsylvania that is deemed unsafe by an inspector is closed. Fracture critical and structurally deficient bridges warrant more frequent inspections, but a bridge that qualifies for both categories does not necessarily make it unsafe, he said.

The Associated Press analyzed data involving 607,380 bridges in the National Bridge Inventory, which are subject to National Bridge Inspection Standards. On a national basis, there are 65,605 structurally deficient bridges and 20,808 fracture critical bridges, according to the most recently available federal government data.

A bridge is deemed "fracture critical" when it does not have redundant protections and is at risk of collapse if a single, vital component fails. A bridge is "structurally deficient" when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition "poor" or worse.

Some 7,795 bridges nationwide fall into both categories -- a combination of red flags that experts say is particularly problematic. The most recent federal data shows Pennsylvania among the top five states with bridges classified as both fracture critical and structurally deficient.

In Pennsylvania, the number of structurally deficient bridges is a little over 4,000, down from some 6,000 several years ago. It has about 1,350 fracture critical bridges, such as the Walt Whitman, PennDOT said.

Pennsylvania has effectively stopped building fracture critical bridges, unless bridge designers are left no other choice, Christie said. That policy change is decades old after the 1983 collapse of a portion of the Mianus River Bridge on Interstate 95 in Connecticut. Three people died after their vehicles plunged 70 feet into the river.

The accident also prompted Pennsylvania to focus on adding secondary beams to a fracture-critical bridge style known as pin-and-hanger assembly, Christie said.